Optical disks represent a significant percentage of the market for data storage of photographic, video, audio and software data. Typically, optical disks have data patterns contained on the disk that can be read from one side of the disk and a graphic display printed on the other side of the disk. Various optical disk formats are available such as readable and writable CDs, DVDs, and other formats.
In order to identify the contents of the optical disk, printed patterns or graphic display information can be provided on the non-data side of the disk. The patterns or graphic display can be both decorative and provide information about the disk's data contents. In the past, commercial labeling has been routinely accomplished using screen-printing methods. While this method can provide label content, it tends to be cost ineffective for the production of less than about 400 disks because of the fixed costs associated with preparing a stencil or combination of stencils and printing the desired pattern or graphic display.
In recent years, the significant increase in the use of optical disks for data storage by consumers has increased the demand to provide customized labels for optical disks. Most consumer labeling methods include either handwritten descriptions or preprinted labels which may be affixed to the disk, but handwritten labels lack a professional appearance while affixed labels may adversely affect the disk performance upon spinning at high speeds.
Recently, a variety of radiation sensitive compositions have been developed for use on optical disks as disk labeling technology. In particular, disk labeling technology exists that can form text and/or graphics directly onto the label side of a CD or DVD using the optical drive's laser and a specially coated disk. The coating on a radiation sensitive disk layer can change color or chemical structure when the dye is exposed to the CD/DVD drive's laser. Accordingly, the disk surface specifically reacts to a particular wavelength emitted by the laser.
Forming an image onto a label side of a disk typically involves several components. These components include an optical print head that selectively outputs the laser light onto track locations on the disk surface to form the spots that make up the labeled image. In addition, a disk with a label side layer containing a radiation sensitive material layer is used. Software is used to manage the imaging process and determine which disk locations will be optically exposed.
Devices which may accept storage media, such as CD's or DVD's, often have a plurality of optical components, including an objective lens, which focus the light source onto the data side or label side of the disk. The objective lens is typically connected to a voice coil motor, which adjusts the position of the objective lens to achieve a desired focus or spot size on the storage medium. The size of a spot on the label side is determined, in part, by the size of the light source spot which can be focused onto the storage medium.
The optical components used for reading or writing to the disk media are costly to manufacture, particularly due to the expense of the voice coil motor used for adjusting the position of the objective lens. The cost of using a voice coil motor and related control circuits in an optical system is difficult to avoid because the optical medium surface is not perfectly smooth, which results in variable distances between the light source and the storage medium itself. While fixed focus system are less expensive due to the use of fewer parts, fixed focus optical systems have not been able to maintain energy focus on the storage medium as the distance between the light source and storage medium changes.